The present invention relates to an exposure illumination apparatus for use in copying machines and more particularly to an exposure illumination apparatus comprising a semi-cylindrical reflector having a quadratic surface and a linear light source, which is employed as a slit exposure illumination apparatus in electrophotographic copying machines.
Conventionally, as linear light sources in slit exposure illumination apparatus of electrophotographic copying machines, cylindrical light sources having comparatively small diameter light emitting portions, such as halogen lamps and flash lamps, are employed. As is well known, the light emitted from such light sources includes visible light and much infrared light.
Therefore, when the above-mentioned type light sources are employed in a slit exposure illumination apparatus, the original to be copied or the contact glass of the copying machine on which the original is placed may be overheated by the infrared radiation, and, in the case of the glass, said heat is ultimately transmitted to the surface of the original. In order to prevent this, a heat reflective filter which is capable of reflecting infrared light while allowing visible light to pass through is disposed in the optical path of the exposure of the original in the copying machine.
This method is unquestionably effective for preventing the original to be copied from being overheated by infrared light. However, infrared light is apt to be diffused within the copying machine by the filter, and consequently the temperature within the copying machine tends to be elevated.
Furthermore, in the case of a light source employing metallic filaments such as tungsten filaments, it is required to supply heat energy in order to cause the light source to emit light therefrom. In order to do this, generally all the required energy is supplied in the form of electric energy.
Therefore, if infrared light emitted from the light source could be returned to the light source and used for said heating, part of the electric energy required could be saved.
In a conventional slit exposure type illumination apparatus, a heat reflective filter is disposed in the optical path of the exposure illumination so that infrared light emitted from its light source is reflected back to the light source by the heat reflective filter. In practice, however, only part of the infrared light is returned to the light source, and the above-mentioned savings have not been attained sufficiently.
Furthermore, the conventional heat reflector is large in size, and when the heat reflective filter is built into the exposure illumination apparatus, the exposure illumination apparatus tends to be over-sized and expensive.